2.00 ECS 1.00 IonsMass Molarity (or concentration) Calculations © Chemworks

2.00 ECS 1.00 IonsMass Molarity is the concentration of a solution. If you take 1 mole of a chemical... and dissolve it in 1 litre of water … the solution has a molarity of 1 mole per litre

2.00 ECS 1.00 IonsMass Molarity has units of moles l –1 1 mole dissolved in 1 litre = 1 moles l –1 So, the molarity depends on: a) the number of moles being dissolved; b) the volume of liquid being used. and 0.5 mole dissolved in 1 litre = 0.5 moles l –1 while 1 mole dissolved in 0.5 litre = 2 moles l –1

2.00 ECS 1.00 IonsMass So, the molarity depends on: a) the number of moles being dissolved; b) the volume of liquid being used. We can simplify this by using a triangle. conc vol moles the volume of liquid (in litres) the molarity or concentration the number of moles

2.00 ECS 1.00 IonsMass Now let’s try two examples …

2.00 ECS 1.00 IonsMass Calculate the molarity of 3 moles NaCl in 2 litres. molarity = moles of NaCl volume (in litres) molarity = 3 = 1.5 moles l –1 2 And a second example … conc vol moles

2.00 ECS 1.00 IonsMass Calculate the molarity of 2 moles NaCl in 500ml. molarity = moles of NaCl volume (in litres) molarity = 2 = 4 moles l –1 0.5 Here are a few for you to try … conc vol moles

2.00 ECS 1.00 IonsMass Calculate the molarity of: 1.5 moles NaCl in 300 ml0.4 moles NaCl in 800 ml molarity = moles of NaCl volume (in litres) conc vol moles molarity = 1.5 = 0.05 moles l –1 0.3

2.00 ECS 1.00 IonsMass Calculate the molarity of: 4.5 moles NaCl in 1500 ml0.4 moles NaCl in 800 ml conc vol moles molarity = moles of NaCl volume (in litres) molarity = 0.4 = 0.5 moles l –1 0.8

2.00 ECS 1.00 IonsMass Calculate the molarity of: 4.5 moles NaCl in 1500 ml1.35 moles NaCl in 450 ml molarity = moles of NaCl volume (in litres) conc vol moles molarity = 4.5 = 3 moles l –1 1.5

2.00 ECS 1.00 IonsMass Calculate the number of moles in: 200 ml of 3 moles l –1 LiCl1.35 moles NaCl in 450 ml conc vol moles molarity = moles of NaCl volume (in litres) molarity = 1.35 = 3 moles l –1 0.45

2.00 ECS 1.00 IonsMass Calculate the number of moles in: 200 ml of 3 moles l –1 LiCl moles = molarity x volume conc vol moles moles = 3 moles l –1 x 0.2 litres = 0.6 moles 100 ml of 0.5 moles l –1 LiCl

2.00 ECS 1.00 IonsMass Calculate the number of moles in: 250 ml of 2 moles l –1 LiCl conc vol moles 100 ml of 0.5 moles l –1 LiCl moles = molarity x volume moles = 0.5 moles l –1 x 0.1 litres = 0.05 moles

2.00 ECS 1.00 IonsMass Calculate the number of moles in: 250 ml of 2 moles l –1 LiCl moles = molarity x volume conc vol moles moles = 2 moles l –1 x 0.25 litres = 0.5 moles 600 ml of 1.5 moles l –1 LiCl

2.00 ECS 1.00 IonsMass Calculate the number of moles in: 150 ml of 0.3 moles l –1 LiCl conc vol moles 600 ml of 1.5 moles l –1 LiCl moles = molarity x volume moles = 1.5 moles l –1 x 0.6 litres = 0.9 moles

2.00 ECS 1.00 IonsMass Calculate the number of moles in: 150 ml of 0.3 moles l –1 LiCl moles = molarity x volume conc vol moles moles = 0.3 moles l –1 x 0.15 litres = moles 25 ml of 6 moles l –1 LiCl

2.00 ECS 1.00 IonsMass Calculate the volume of a: 2 moles l –1 LiCl solution, containing 0.5 moles KCl conc vol moles 25 ml of 6 moles l –1 LiCl moles = molarity x volume moles = 6 moles l –1 x litres = 1.5 moles

2.00 ECS 1.00 IonsMass Calculate the volume of a: 2 moles l –1 LiCl solution, containing 0.5 moles KCl volume = moles molarity conc vol moles volume = = 0.25 litres 0.3 moles l –1 LiCl solution, containing 0.06 moles KCl

2.00 ECS 1.00 IonsMass Calculate the volume of a: 5 moles l –1 LiCl solution, containing 0.5 moles KCl conc vol moles 0.3 moles l –1 LiCl solution, containing 0.06 moles KCl volume = moles molarity volume = = 0.2 litres

2.00 ECS 1.00 IonsMass Calculate the volume of a: 5 moles l –1 LiCl solution, containing 0.5 moles KCl volume = moles molarity conc vol moles volume = = 0.1 litres 1.5 moles l –1 LiCl solution, containing 9 moles KCl

2.00 ECS 1.00 IonsMass Calculate the volume of a: 4 moles l –1 LiCl solution, containing 0.8 moles KCl conc vol moles 1.5 moles l –1 LiCl solution, containing 9 moles KCl volume = moles molarity volume = = 6 litres

2.00 ECS 1.00 IonsMass Calculate the volume of a: 4 moles l –1 LiCl solution, containing 0.8 moles KCl volume = moles molarity conc vol moles volume = = 0.2 litres 2.6 moles l –1 LiCl solution, containing 7.8 moles KCl

2.00 ECS 1.00 IonsMass Calculate the volume of a: conc vol moles 2.6 moles l –1 LiCl solution, containing 7.8 moles KCl volume = moles molarity volume = = 3 litres

2.00 ECS 1.00 IonsMass Well done!